Transmissions for industrial motor vehicles often have twelve, sixteen or more gears. Such multi-ratio transmissions are mostly configured as multi-group transmissions which divide into a front-mounted group, a main group and a range group. Most of these transmissions have an automated gear-shifting device in order to simplify the complex shifting cycle created by the multiplicity of gears. The gear shifts in the main transmission are manually carried out by the driver. Multiple gear-shifting elements are also provided in the gear-shifting process, which have to be harmonized with each other, and different protection mechanisms to protect the transmission from erroneous gear shifts. At the same time, in traditional models the range group is, as a rule, synchronically shifted with the aid of gear-shifting elements, locking synchronization mechanisms or powershift clutches.
German patent application P 100 29 497 has disclosed a pneumatic gear-shifting device with protection mechanisms from erroneous movements in the gear selection. A transmission is described with a mechanical interlock where the selector rods in the main transmission are blocked mechanically or via a locking bolt when the selector rods of a group transmission are not in one of their two final positions. This occurs via adequately laid out slanting on the selector rod of the group transmission. This function should ensure that the gear shift in the group transmission is terminated before the main transmission gear shift and the synchronizer process connected therewith follow. There is further provided a pneumatic-mechanical gate interlock which is activated by one signal of the output shaft rotational speed, in order to block the selection movement for shifting an inadmissible gear. Between the individual shift gates, a bump detent is further provided for insurance against inadvertent shifting of the group transmission.
Those protective precautions and mechanisms, however, act disadvantageously on the shifting comfort. Strong manual shifting forces, interfering shifting noises and a shifting movement not flexible enough are produced. The driver often finds a bump detent in the shift gates irritating. In addition, the protective measures cause the increase of the total costs for the transmission.
The individual groups of the multi-group transmission certainly can be shifted by an external rotational speed command without consequent problems. But such successive shifting of the individual groups result in extremely long shifting periods. In a 16-gear transmission for shifting from the 8th gear to the 9th gear, the front-mounted group is first shifted with participation of the transmission brake from the low-speed ratio to the high-speed ratio of the transmission. Thereafter, by the actuation of a clutch, the main transmission is shifted from the fourth ratio step to the first ratio step and finally from the slow ratio to the quick ratio range group.
The problem on which this invention is based is to provide for gear a method shifting a multi-group transmission which abbreviates the shifting periods, reduces the shifting force required, prevents shifting noises and simplifies the gear shifting process altogether.
This problem is solved by a gear-shifting method according to the characteristic features of claim 1. Other variations are explained in the sub-claims.